Method of making copper-colored ruby glass

ABSTRACT

A process for making copper-colored ruby glass in which a copper-tin alloy (bronze) is wetted with sodium silicate water glass solution and introduced into a soda-lime glass batch, together with potassium nitrate, as an oxidizing agent, and in the absence of reducing agents, melted at up to 1,480*C and in which ruby-red coloration appears upon rapid cooling.

United States Patent Simonfi et a1.

[ Dec. 18, 1973 METHOD OF MAKING COPPER-COLORED RUBY GLASS Inventors:Paul Simonfi, Turda; Viorel Cristea,

Timisoara, both of Romania Assignee: Fabrica de Sticlarie Turda, Turda,

Romania Filed: Apr. 24, 1972 Appl. No.: 246,901

Related US. Application Data Continuation-in-part of Ser. No. 207,673,Dec. 13, 1971, abandoned, which is a continuation of Ser. No. 812,880,Apr. 2, 1969, abandoned.

References Cited UNlTED STATES PATENTS 3/1970 Hammer et al. 106/522/1941 Dobrovolny et a1 106/52 FOREIGN PATENTS OR APPLICATIONS 101,63612/1955 U.S.S.R. 995,576 6/1965 Great Britain 65/134 OTHER PUBLICATIONSWeyl, W., Coloured Glass-pub. 1967 by Society of Glass Technology,Sheffield, England, pp. 425-432.

Primary Examiner-Helen M. McCarthy Att0rneyKarl F. Ross [5 7] ABSTRACT Aprocess for making copper-colored ruby glass in which a copper-tin alloy(bronze) is wetted with sodium silicate water glass solution andintroduced into 4 a soda-lime glass batch, together with potassiumnitrate, as an oxidizing agent, and in the absence of reducing agents,melted at up to 1,480C and in which ruby-red coloration appears uponrapid cooling.

3 Claims, No Drawings METHOD OF MAKING COPPER-COLORED RUBY GLASSCROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of our application, Ser. No. 207,673 filed 13 Dec.1971 as a continuation of application Ser. No. 812,880 filed 2 Apr.1969, both now abandoned.

FIELD OF THE INVENTION Our present invention relates to a method of or aprocess for producing ruby glass and, more particularly, to a method ofor a process for the coloring of soda-lime glass so as to impart aruby-red coloration thereto.

BACKGROUND OF THE INVENTION The production of ruby glass by adding acoppercontaining colorant to a batch of otherwise uncolored glass, hasbeen described in the literature. For example, it is known to addcuprous oxide or cupric oxide or copper sulfate to the glass mixture,generally under reducing conditions brought about by the introduction ofreducing agents and controlling the melting and cooling so that, it isbelieved, colloidal particles of copper are formed in the glass to yieldthe desired red or ruby coloration. Because of the control required, ithas generally been a practice to use glass fritting techniques or towithhold the colorant until the last parts of the process. We shouldalso mention that it is known to obtain a coloration of glass byintroducing powdered coppertin alloys (bronzes) in the presence ofreducing agents, into the glass melt.

These techniques have generally been found to be unsatisfactory sincethe presence of a reducing agent does not allow large amounts ofcolorant to be introduced. Furthermore, it is difficult to maintain thecritical atmosphere and melt temperature to avoid undesirable colordeviations arising from partial oxidation of the copper whereby blue orgreen coloration is obtained.

OBJECTS OF THE INVENTION It is an important object of the presentinvention to provide an improved method of or process for the productionof ruby-colored glass, especially rubyred sodalime glass, at low cost,with intense uniform coloration and with freedom from discoloration byoxidation of copper-containing materials.

SUMMARY OF THE INVENTION These objects and other which will becomeapparent hereinafter are attained, in accordance with our invention,which provides for the incorporation in a sodalime glass, for example, acolorant consisting of a bronze of the type already described but whichhas been coated with sodium silicate, the function of which is describedin greater detail below.

The starting material is preferably a soda-lime glass made by anyconventional process and of any conventional composition as described,for example, in the art. A typical soda-lime glass may have 78 to 45parts by weight of granitic materials (e.g. crushed granite), to 20parts by weight of sodium silicate, lime or limestone in an amount of 5to parts by weight and, if desired, any additives intended to producespecific characteristics of the glass. Such additives may be manga- 7 to18 percent y weight 0 to 5 percent y weight.

0 to 5 percent y weight.

percent 35 percent y weight barium oxide selenium A preferredcomposition is:

SiO 72-75 percent by weight Na O 15-18 percent K 0 1-3 percent CaO 6-8percent B 0 0.5-] percent The conditions and procedures for making thebase glass are conventional and may be found at page 245, Handbook ofGLASS MANUFACTURE, Odgen Publishing Co., New York, N. Y.

According to the principles of the present invention, in a preferredembodiment, the bronze consists of a white crystalline alloy containing60 percent by weight of copper and 40 percent by weight tin, togetherwith the usual impurities, zinc, aluminum, iron phosphorus and sulfate.The alloy is coated with water glass, a silica-containing liquid with aslightly opalescent aspect, a density at 20C of 1.36 to 1.38, a minimumSiO content of 25 percent by weight, up to 1.0 percent by weight of ironand aluminum oxides, a maximum of Fe o content of 0.15 percent byweight, a maximum calcium oxide content of about 0.15 percent by weightand a maximum sodium chloride content of 0.01 percent by weight.

Advantageously, the alloy can be added in powdered form after coatingwith the water-glass solution, in any quantity which will provide thedesired depth of coloration.

While we do not wish to be bound by any theory with regard to the modeof operation of the present invention, we believe that the sodiumsilicate waterglass after drying functions as a sheath for the bronzepowder during the glass-melting process.

The literature is in dispute on the mechanism of the formation of theruby-red coloration with some authors in the field holding that thecoloration is caused by metallic copper in colloidal-particle form whileothers urge that the coloration derives from the presence of cuprousoxide in the glass. Again, we wish in no way to contribute to thiscontroversy although we have found that surprisingly improved resultsare obtained when an oxidizing agent, especially potassium nitrate, ispresent and the glass mass is free from reducing agents.

According to yet another feature of the present invention, the coppertin-containing bronze is used in an amount between 1.5 and 3 percent byweight of the soda-lime glass mass prior to melting. Advantageously, 0.5to 2 percent by weight of saltpeter (potassium nitrate) is provided and200 g of sodium silicate (waterglass) are used to wet 1 kg of the alloypowder. (Approximately 0.25 to 1 percent by weight of the glass mass issodium silicate). The alloy powder is mixed with saltpeter (potassiumnitrate) and the powder mixture is treated with the sodium silicate.

We have found it to be desirable to melt the mixture of glass-formingsubstances with the copper tin-bronze mixture, after the latter has beencoated with the sodium silicate, in crucibles at temperatures up tol,480C for a period of 14 16 hrs in a weakly oxidizing atmosphere.

Experiments have shown that a film of waterglass forms around the alloyparticles and expands as the temperature rises to 300C by loss of water,the coated particles increasing in volume. As a result, the coatedparticles remain distributed in the mixture, without sinking to thebottom because of higher density until formation of the glass melt andaid in the diffusion of the alloy into the glass.

The sodium silicate coating, formed by the water glass on and around thealloy particles, melts'at about l,088C, somewhat after the melting ofthe alloy, and thus constitutes a pocket in which the alloy is retainedin suspension in the glass Melting is preferably carried out using anoxidizing flame for initial melting, followed by a neutral to slightlyoxidizing flame during the'latter steps. It has been found to bepossible to retard the formation of the ruby color by increasing thequantity of saltpeter (ptassium nitrate) and to accelerate coloration byreducing the quantity of saltpeter. In general, when the alloy and thepotassium nitrate are added in increments, the rate of appearance ofcoloration may be controlled by varying the quantity of potassiumnitrate supplied in the batch.

Of special importance is the fact that the furnace environment andconditions appear to have little if any effect on the color, that thequantities of colorant and potassium nitrate and proportions thereofdetermine the hue with high precision and the coloring of the glass ishighly reproducible.

The ruby glass is preferably cast into bars of rectangular cross-sectionof a width and thickness of X 3 cm and then rolled, annealed and usedfor ruby thin-layer glass applications.

EXAMPLE I the mass and does not form a pool on the bottom.

The tin bronze according to the present invention should contain about60 percent copper and 40 percent tin. This, of course, is the preferredcomposition, although we may use tin bronzes containing 50 percentcopper /50 percent tin to perent copper/ 30 percent tin, all proportionsby weight. Surprisingly, the trace impurities zinc, aluminum, iron,phosphorous and sulfur remain about the same for any given tin-alloycomposition and ensure constancy of coloration. The hues obtained withone batch or alloy mass do not differ materially from the next.

According to another feature of the invention, the basic glass mass isintroduced into a basin furnace at a temperature of about l,450C,whereupon the alloy coated with waterglass (sodium silicate) isintroduced in a powdered form together with the saltpeter or potassiumnitrate. The mixture is introduced in three to four steps with completedispersal being permitted between the steps, whereupon the furnace ismaintained at the relatively high temperature of l,450 to l,480C for aperiod of about 3 hours and until air bubbles are no longer found in themelt. The melt is then being cooled to processing temperatures of aboutl,200C and the mass drawn into sheets or cast into bars. The ruby-redcoloration appears upon rapid cooling.

6 percent by weight CaO 1 percent by weight B 0 3 percent by weight ofthis mass of a tin bronze consisting of 60 percent by weight copper and40 percent by weight tin is prepared by turning a bar of the alloy andcrumbling the tumings to a particle size of 5 microns to 50 microns. Theparticles are mixed with 1 percent (by weight of the glass mixture) ofpotassium nitrate powder and the mixture is coated with sodium silicate(waterglass) until the alloy particles are encased in a sheath of thelatter. The resulting mixture was divided into four equal portions byweight for addition to the glass batch at intervals.

After introducing one of the portions into the original glass batch, thelatter is melted and brought to a temperature of l,480C with anoxidizing flame, the temperature being measured at the flame. After thebatch has melted, a second portion of the additive is introduced,whereupon the temperature is maintained between l,450C and 1,480C for aperiod of 3 hours. The third portion of the additive is introduced after1 hour and the fourth portion after 2 hours. At the end of about 3hours, no more glass bubbles are observed in the mass. The glass iscooled to 1,200C and drawn into bars of a rectangular cross-section 3 X5 cm on a side. The glass bars are annealed in the conventional fashion.The product has a well-defined bright ruby-red coloration from whichoverlapped glassware may be obtained.

EXAMPLE II A glass batch of the following composition is used:

72 percent by weight SiO 18 percent by weight Na O 2 percent by weight K0 7 percent by weight CaO 1 percent by weight B 0 The aforementionedbatch was melted in crucibles at a temperature of 1,480C under theweakly oxidizing atmosphere. The additive consisted of 0.5 percent byweight (of the glass batch) potassium nitrate, 1.5 percent by weight60140 copperztin bronze and sufficient sodium silicate to coat theparticles as described. The mixture was added in four portions atintervals of 3 to 4 hours, whereupon glass bars were drawn as alreadydescribed.

EXAMPLE Ill,

Using the method of Example ll, ruby-red glass bars for carving,layering upon other soda-lime glass and other hot working is producedfrom a glass batch of the following composition:

73.5 percent by weight SiO 16 percent by weight Na O 3 percent by weightK 7 percent by weight CaO and 0.5 percent by weight B 8 The colorantconsisted of 60:40 copperztin bronze in an amount of 2 percent by weightof the glass batch and 1 percent by weight of the glass batch ofpotassium nitrate. in this case, the sodium silicate was used to coatonly the metal particles and the potassium nitrate was then mixedtherewith.

Throughout the treatment in Examples I ill, the melt was carried outwithout reducing agents.

We claim:

1. A process for producing copper ruby glass comprising the steps of:

coating particles of a copper tin alloy powder consisting essentially of50 percent by weight to 70 percent by weight copper and 50 percent byweight to 30 percent by weight tin with sodium silicate waterglasssolution;

mixing the coated alloy particles with potassium nitrate powder, andadding to a soda-lime glass batch mixture, said soda-lime glass mixtureconsisting essentially of 72 to 75 percent by mixture; SiO 15 to 18percent by weight N320, l to 3 percent K 0, 6 to 8 percent C210 and 0.5to l percent by weight B 0 being free from reducing agents, and in whichthe alloy powder is L5 to 3 percent, sodium silicate 0.25 to l percent,and potassium nitrate about 0.5 to 2 percent, all by weight of the glassmixture; melting the resulting mixture in a weakly oxidizing atmosphereand heating same to a temperature of substantially l,450C to l,480C fora period of substantially 14 to 16 hours to form a melt; and

cooling said melt to produce the ruby colored glass body.

2. The process defined in claim 1 wherein the mixture of said coatedalloy particles, said potassium nitrate and said soda-lime glass mass isintroduced in three to four increments into a furnace for melting andheating therein.

3. The process defined in claim 1 wherein said alloy consists ofsubstantially 60 percent by weight copper and 40 percent by weight tin.

2. The process defined in claim 1 wherein the mixture of said coatedalloy particles, said potassium nitrate and said soda-lime glass mass isintroduced in three to four increments into a furnace for melting andheating therein.
 3. The process defined in claim 1 wherein said alloyconsists of substantially 60 percent by weight copper and 40 percent byweight tin.